1. Field of the Invention
The present invention relates to a method of producing molding members for automobiles, formed at least partly of a synthetic resin material.
2. Description of the Related Art
An automobile employs various kinds of elongate molding members formed at least partly of a synthetic resin material, such as drip molding members, front and rear window molding members, etc. Of these, the drip molding member extends along the front pillar and the side edge of the roof panel of the vehicle body, while front and rear window molding members extend respectively along the periphery of the front and rear window plates, i.e. along the front and rear pillars and the front and rear edges of the roof panel. A variety of requirements are imposed on the molding members, mainly from design and/or functional viewpoint, resulting in an increased demand in the automobile industry for molding members whose cross-sectional shape varies in the longitudinal direction.
More particularly, one proposal is directed to a window molding member having side portions with a first predetermined cross sectional shape, an upper portion with a second predetermined cross-sectional shape, and corner portions arranged between the side and upper portions, where the cross-sectional shape changes gradually from the first to the second.
Another proposal is directed to a drip molding member composed of a core element in the form of a metal strip which has been shaped into the desired cross-sectional shape, as well as upper and lower lip elements of synthetic resin material which are integral with the core element and molded such that the core element is partly exposed to, and visible from the outside as a longitudinally extending ornamental portion with a metallic luster. The lower lip element is of a cross-sectional shape that is substantially constant throughout the entire length, while the upper lip element has a pillar portion with a relatively wide first cross-sectional shape, a roof portion with a relatively narrow second cross-sectional shape, and a corner portion between the pillar and roof portions, where the cross-sectional shape changes gradually from the first to the second.
To produce elongate molding members whose cross-sectional shape varies in the longitudinal direction, it has been a conventional practice to use a process which includes preparation of the core element by shaping the raw metal strip into the desired cross sectional shape with a roll forming machine, press machine, etc., placing each core element in the mold of an injection molding machine, and subsequently molding the synthetic resin material into the desired configuration. With such a process, however, since the entire core element of the elongate molding member has to be completely accommodated in the mold, the molding machine as a whole becomes very bulky and requires a substantial space in the factory. Moreover, the process involves relatively complex steps with which the molding members can be produced only one by one, and it is thus difficult to improve the productivity.
Another possibility for the production of such molding members is to physically divide each molding member into first and second extruded portions with the respectively predetermined cross-sectional shapes, which are connected with each other either by an injection molding process or by using a separate connection piece. However, connection of the two portions by means of the injection molding accompanies formation of undesirable burrs along the junctions and resultant deterioration in the appearance, while use of the separate connection piece results in the increased number of the required components and assembly steps.